Page:Natural History, Reptiles.djvu/164

156 this kind of progressive motion.” “An observation of Sir Joseph Banks during the exhibition of a Coluber of unusual size first led to this discovery. While it was moving briskly along the carpet, he said he thought he saw the ribs come forward in succession, like the feet of a caterpillar. This remark led me to examine the animal's motion with more accuracy, and on putting the hand under its belly, while the Snake was in the act of passing over the palm, the ends of the ribs were distinctly felt pressing upon the surface in regular succession, so as to leave no doubt of the ribs forming so many pairs of levers, by which the animal moves its body from place to place.”

It is doubtless by the expansion of these rib-feet, and by the application of them alternately to the surface on which they move, that Serpents are able to glide with facility up the trunks, and along the branches of trees, a feat which we have seen the Colurbidæ of America and the West Indies perform repeatedly, not (as absurdly represented in engravings) by encircling the tree in spiral coils, but gliding along with the body extended, exactly as a caterpillar crawls, but with far greater speed.

The earth is the sphere of activity of by far the greatest number of the Serpent races: they inhabit various situations, some frequenting woods, others heaths, and many preferring deserted buildings, old walls, and heaps of stones. A few species reside permanently among the foliage of trees; and others there are, which are truly aquatic, roving through the ocean even at considerable distance from the shores. These have the